Difference between ORF and Exon


The ORF (open reading frame) is a nucleotide sequence that begins with the start codon and ends at the stop codon. A start codon usually initiates the translation process. Also, a transcription terminator site is seen beyond the ORF stop codon. If the transcription ends before the stop codon, it can result in incomplete protein synthesis. Also, an ORF region need not always lead to translation.

Long ORFs are used as classic evidence to find the protein-coding region of DNA. Certain short ORFs can lack protein-coding genes, and thus they create functional peptides.


Exons are coding sequences that correspond to both the DNA of a gene and its RNA transcript. Here, RNA splicing helps in the removal of introns. After splicing, the exons join with one another to form a mature mRNA.

The exon sequence includes both protein-coding regions and also the UTR (untranslated regions). Certain non-coding RNA transcripts can have both introns and exons.

Difference between ORF and Exon



It is a DNA sequence that stretches from the start to the stop codon.

It is the protein-coding part of a gene.

It has a start codon (AUG), a coding sequence and a terminal stop codon.

It is a nucleotide sequence of varied lengths that generally have introns on either side in a primary transcript.

Explore: Transcription of DNA and Central Dogma

Frequently Asked Questions on Difference between ORF and Exon


What are introns?

Introns are the non-coding region of a DNA sequence or RNA transcript. This region is usually eliminated by RNA splicing to create a mature RNA. There are certain sequences called the exitrons that have features of both exons and introns. Still, they are considered as introns.


What are transcription and translation?

Transcription is a process by which a sequence of DNA is transcribed into mRNA. Later, the ribosomes decode the mRNA to synthesise protein molecules. This process is called translation.


What is the size and distribution of the exon?

The human genome has approximately 1.1% exons and 24% introns. The remaining are IGR (intergenic region). Some of the smallest exons have only two base pairs. The longest exon has been found to have 11555 base pairs.

Also Read: Differences between Exons and Introns

Keep exploring BYJU’S Biology for more exciting topics.


Leave a Comment

Your Mobile number and Email id will not be published.